Steam Boiler

The design soot blowing system should
furnish well experienced and approved steam jet type sootblowers for the
superheater, generating bank, economizer and air heater. The design soot
blowing system should arrange the sufficient number of sootblowers for the above
mentioned equipment.

If additional soot blowing
equipment is necessary to maintain the proper surface conditions of
superheater, generating bank, economizer, or air heater, additional equipment
with all piping and wiring should be furnished without any addition to the
contract price during the guaranteed period.

A complete soot blowing system
consisting of all controls, actuators, piping, valves, control panels,
including all necessary starters, switches, relays, protection devices, etc., should
be provided. Steam from high pressure auxiliary steam header should be used as the
cleaning medium. An air operated isolating valve controlled from the remote
control panel should be provided to allow isolation of the soot blowing steam.

Complete remote control system
for each sootblower, including all switches, relays, signal lamps, sequences,
etc., should be provided and installed in the central control room to supervise
operation of blowers.

The system should be able to
allow local manual operation of each sootblower in case of test or failure of
remote control system. The remote control panel should be of the mimic type
suitable for flush mounting. The panel should be complete and fully wired and
tubed with clearly identified terminal blocks and strips.

The panel should be mounted on
the auxiliary control panel in the central control room. All motor starters for
the boiler sootblowers should be furnished. Motor starters should be of magnetic type
mounted on each sootblower with thermal trip relays and start-stop push buttons
for local operation.

Retractable sootblowers should be
provided with a hand crank or drive nut for withdrawing the lance tube in case
of power failure. Sootblowers should be installed in such a manner as to permit
boiler expansion without binding or unbalanced loading. A complete system of
sealing air piping should be furnished to seal the wall sleeves if necessary.

A complete system of aspirating
air piping to permit removal of blower of should be furnished if necessary.
Sealing air and aspirating air piping should have flexible hoses to permit
boiler expansion without binding.

Any drain attack due to soot
blowing on superheater, generating bank, economizer and air heater element should
be absolutely prevented. Special consideration should be given to the method of
efficient draining and heat insulation. Any other cleaning system on heating
surfaces of flue gas side should be given a special consideration and should be
approved by the engineer.

Construction of LP and HP Heater
should be performed as procedure and design. The selection of LP heater
materials and method of construction remains with the design although the use
of shells with a minimum number of joints, welded tube plate to channel joint,
and welded feedwater pipe attachments are preferred. The corrosion resistance
of the proposed tube material selection should make due allowance for the
oxygen content that may prevail in the LP feedwater, particularly at low load
and during start up.

The LP and HP heater should be of
the conventional U tube and shell type for which the selection of tube and tube
plate material, and their method of attachment should be described. The
proposed selection of materials for the tubes, tube plate or header should be
in accordance with Code and Standards, provided together with full details of
the method of tube attachment.

This selection should be based on
service experience with waterside velocities not exceeding previous good
service experience. All tubes should be produced from single lengths of tubes
and be hydraulically tested to the requirements of ASME standard or equivalent
standard.

The bled steam inlets of both the
LP and HP heaters should incorporate provisions to prevent erosion, impingement
and vibration damage of the tubes by either steam or water. All bled steam and
drain inlets should incorporate arrangements to prevent direct impingement of
fluid against the tube nest.

The method of attaining access
into the channel or headers should be described, to permit inspection and
plugging of all tube ends. With divided channel designs, details of the
construction and attachment of the dividing wall or chamber to the channel should
be provided.

For both the LP and HP surface
type heaters, only designs with proven service reliability whilst of similar
size and rating should be proposed and reference listings should be made
available during the contract.

Design surface Type LP and HP heater
should be described with reference to sectional arrangement drawings. These
drawings should be representative in terms of heater disposition, channel
division plate details, baffling arrangements, the location of any
de-superheating and drain cooling sections arid their shrouding, etc.

The design surface Type LP and HP
heater must be performed by manufacturer which has relevant and successful
experience with the type of heaters being proposed. Heaters are required to
last the life of the station with minimal maintenance. The design surface Type
LP and HP heater should therefore describe the design features incorporated
into the design of the feed water heaters to minimize or eliminate problems of:

The design daerator should
consist of the dearating unit and a feed water storage vessel. A feed water
storage vessel should be provided within the feed water heating system. The
dissolved oxygen content in the feed water effluent from the heater should not
be more than 0.007 mg/liter at any load condition, measured in accordance with
the "Method and Procedure for the Determination of Dissolved Oxygen"
of the Standards of the Heat Exchange
Institute. The feed water storage vessel should be integrated with a deaerating
unit to fully de-aerate the feed water, if an alternative water chemistry
regime is proposed the design should substantiate his provisions for control of
dissolved oxygen in the feed water system.

Whichever arrangement of feed
water / deaeration vessel in the design deaerator or feed water storage vessel
to provide a full description of the normal function, including:

Level indication and level
control

Conditioning of feedwater prior
to start-up (cold start)

Flows of condensate, bled steam,
auxiliary heating steam

System responses to transient
conditions

Any specific arrangements
proposed for part load operation

Disposal of scrubbed or vented
non condensable gases

The design deaerator or feed
water storage vessel should state the provision for deaeration and heating the
stored water on plant starts when the LP heater is out of service. The description
should also describe the provision included to monitor and control the
condensate level within the storage tank and any recirculation system if
necessary to ensure homogenous conditions in the stored water.

The feed water storage vessel should
be located at or as close to the turbine operating floor level as possible,
consistent with satisfying the feed pump net positive suction head (NPSH)
requirements. The tank should store a minimum quantity of feed water
corresponding to 7 minutes of rated (MCR) feed water flow or that quantity of
feed water which should permit a controlled and safe shut down of the boiler,
whichever is greater and assuming that the condensate is initially at the
normal working level.

The feed water storage vessel should
be designed to operate with freedom from condensate surging and vessel vibration.
The freeboard above the top of the working level range should be sufficient to
accommodate the total condenser hot well content with margin.

Boiler feed pump leak-off returns
should be introduced into the feed water storage tank in a controlled manner to
prevent damage from high velocity evolved steam or water impingement. At all
other points when steam or water enters the deaerator / feed water storage
vessel, suitable precautions such as baffles or diffusers should be provided to
prevent direct impingement on the tank plates, internals or water surface,
internal baffles should be arranged within the feed water storage tank to
prevent surging of the condensate.

Provisions to protect the steam
turbine from the risk water induction arising from any bled steam pipe work
connecting the deaerator / feed water storage vessel should be as stated in
Section "Bled Steam supply Lines".

The deaerator should be of the
spray/tray type and should include storage tank, supports, vent condenser and
fittings. The design should be to the Heat Exchange Institute standard and
suitable for full vacuum.

The deaerator should be designed
and arranged for the efficient removal of non-condensable gases from the feed
water under all conditions of operation, including the admission of auxiliary
steam during starting and low temperature condensate under fault or restart
conditions.

If a part load deaerator is
offered then the design should include a full description of the start-up and
operation with increasing load up to full load on the steam turbine-generator.

The design deaerator or feed
water storage vessel should describe features of the deaerator head which
facilitate the removal of non-condensable gases from the circulating feed water
and the provision if any, for recovering heat from the vented gases and vapor.
Deaerator level indicators and alarms should be provided in the CCR, these
alarms should be fully functional at all times when the plant is available for
operation, including periods when the plant is on standby duty.

Safety valves should be provided
to protect the deaerator and feed water storage vessel from over pressure from
any source. All parts of the deaerator exposed to oxygen or corrosive gases should
have an adequate corrosion allowance or be of corrosion resistant materials.

Requirement design of tubes is
made to make sure design tube can be used in certain temperature and pressure
in steam boiler. Tubes are one pressure parts. These provisions should apply to
any tubular pressure part that is either exposed over much of its length to hot
gases for purposes of heat transfer or is directly butt welded to such a
tubular pressure part.

Requirement design of tubes should
comply with the requirements of the ASME Boiler and Pressure Vessel Code,
Section I, Power Boilers. The calculation of tube thickness should be based on
ASME BPV Section I.

The requirement design of tubes should
describe the design basis for controlling mechanical wastage (eq. grit and soot
blower erosion) and chemical wastage (e.g. fireside corrosion, dew point
corrosion) of tubing. During the design phase, the requirement design of tubes should supply details
of the wastage provision for each tube design.

Membrane panel construction should
be either by a fusion welded fin or integral fin method. Resistance welded fin
construction will not be allowed. No tube bend should contain a circumferential
weld. Parallel down-flow circuits subject to significant variations in heat
absorption and/or resistance to flow between these circuits should be avoided.
A staggered arrangement of tubes in the gas pass should not be used.

Durable caps suitable for
transportation should be provided on each end of the tubes to prevent damage
and rust on inside surface of tube and to prevent entry of debris. Corrosion or
erosion margin of tube thickness should be provided for the boiler tubes.